1. Field of the Invention
The present invention relates to an injection molding machine having an assembly for vibration processing with which pressurization or cutting work such as gate cutting can be conducted by means of locally applying vibration during cooling of the resin injected into the cavity in a mold.
2. Background Art
Such injection molding machines are known and are used for a variety of processing operations such as punching, gate cutting, and partial compression on a synthetic resin and improvement of flowability of the resin by means of locally applying vibration to the resin in a mold at a vibration frequency of approximately 10 Hz.
The conventional injection molding machine comprises a movable mold half which is arranged in a movable manner relative to a stationary mold half, and a vibratory plate which is mounted within the movable mold half. A desired number of vibratory pins are secured onto the front surface of the vibratory plate with a distal or tip end thereof facing the cavity in the mold. The vibratory plate is abutted against vibratory rods equipped in a vibration generator operated by hydraulic pressure. The vibratory plate is vibrated back and forth by using return springs which generate a reaction force to locally oscillate the resin within the mold by using the vibratory pins during the processing of resin.
The conventional injection molding machine of the type described uses a proportional reducing valve or a servo valve to apply a vibratory force only in an advancing or forward direction. This causes the necessity to use the above-mentioned return springs to generate the reaction force in order to oscillate the resin. The return spring has only a limited level of response, which restricts the vibration frequency up to, about 10 Hz. In addition, there is a problem of vibration transfer loss from the vibratory rods to the vibratory plate with the conventional machine causing difficulties in operation at a high vibration frequency. Another problem is the difficulty in controlling the accurate positioning of the vibratory pins relative to the resin.
A typical injection molding indispensably requires ejector pins to remove molded products from the mold after the mold is opened. These ejector pins are projected from an ejector plate. For this purpose, the molding machine having an assembly for vibration processing contains the vibratory plate along with the ejector plate within the movable mold half. Such a construction makes it necessary to ensure a space for moving both plates. In addition, the plates should be assembled in such a manner that they do not interfere with each other. Therefore, the conventional injection molding machine is likely to have more complicated internal structure as compared with typical injection molds.